Composite Action Step Markers

[ericsciple]

Summary

Emit ##[start-action] / ##[end-action] markers in the log stream around each nested step inside a composite action. The UI parses these markers to render collapsible regions, giving users visibility into individual steps that were previously hidden in a single opaque log blob.

Design

The runner writes ##[ markers directly to the log stream via ExecutionContext.Output(), bypassing the logging command pipeline. No new :: logging command is registered. Users cannot emit these markers from scripts.

Marker format

##[start-action display=<step-display-name>;id=<step-id>]

... step output ...

##[end-action id=<step-id>;outcome=<result>;conclusion=<result>;duration_ms=<ms>]

• id — the step's ContextName (from YAML id: or auto-generated with __ prefix)
• outcome — raw result before continue-on-error is applied
• conclusion — final result after continue-on-error
• duration_ms — wall-clock milliseconds (0 for skipped steps)

Nested composites use dot-separated IDs (e.g. outer.inner-step) to keep each step globally unique.

Feature flag

Gated behind actions_runner_emit_composite_markers (job message variable) with ACTIONS_RUNNER_EMIT_COMPOSITE_MARKERS env var fallback (for internal testing only).

Injection prevention

OutputManager.OnDataReceived replaces ##[start-action and ##[end-action from user process stdout/stderr with ##[\start-action and ##[\end-action. This preventing users from injecting fake markers. The runner's own markers bypass OutputManager entirely since they're written via ExecutionContext.Output() directly.

[ChristopherHX]

I know this is a draft and I am not part of GitHub, tested this interesting thing anyway

[ChristopherHX]

display Name is wrong in composite even if not using expressions, this value is updated later again as this may change if this depends on a changing context variable:

(Logs generated with custom cli tool + env variable)

Currently looks like in the log the displayname is not the expected one

[.github/workflows/test.yml / _] Running: Run ./
| Prepare all required actions
| ##[group]Run ./
| ##[endgroup]
| ##[start-action display=run;id=__run]
| ##[group]Run echo "Hello, World"
| echo "Hello, World"
| shell: /bin/bash --noprofile --norc -e -o pipefail {0}
| ##[endgroup]
| Hello, World
| ##[end-action id=__run;outcome=success;conclusion=success;duration_ms=44]
| ##[start-action display=run;id=__run_2]
| ##[group]Run echo "Hello, World"
| echo "Hello, World"
| shell: /bin/bash --noprofile --norc -e -o pipefail {0}
| ##[endgroup]
| Hello, World
| ##[end-action id=__run_2;outcome=success;conclusion=success;duration_ms=37]
[.github/workflows/test.yml / _] Succeeded: Run ./

Action

runs:
  using: composite
  steps:
  - name: Hello World
    run: echo "Hello, World"
    shell: bash
  - run: echo "Hello, World"
    shell: bash

Minimally this is required for this to be acceptable for me as an actions user.

Suggested change

	ExecutionContext.Output($"##[start-action display={EscapeProperty(SanitizeDisplayName(step.DisplayName))};id={EscapeProperty(stepId)}]");
	step.TryUpdateDisplayName(out _);
	ExecutionContext.Output($"##[start-action display={EscapeProperty(SanitizeDisplayName(step.DisplayName))};id={EscapeProperty(stepId)}]");

After Constant Hello World is the display name or the fallback

[.github/workflows/test.yml / _] Running: Run ./
| Prepare all required actions
| ##[group]Run ./
| ##[endgroup]
| ##[start-action display=Hello World;id=__run]
| ##[group]Run echo "Hello, World"
| echo "Hello, World"
| shell: /bin/bash --noprofile --norc -e -o pipefail {0}
| ##[endgroup]
| Hello, World
| ##[end-action id=__run;outcome=success;conclusion=success;duration_ms=35]
| ##[start-action display=Run echo "Hello, World";id=__run_2]
| ##[group]Run echo "Hello, World"
| echo "Hello, World"
| shell: /bin/bash --noprofile --norc -e -o pipefail {0}
| ##[endgroup]
| Hello, World
| ##[end-action id=__run_2;outcome=success;conclusion=success;duration_ms=27]
[.github/workflows/test.yml / _] Succeeded: Run ./

---

Don't you need to expand the proposal with an update displayname command additionally to start-action or postpone issueing this log info.

runner/src/Runner.Worker/StepsRunner.cs

Lines 195 to 199 in 6680090

	// This is our last, best chance to expand the display name. (At this point, all the requirements for successful expansion should be met.)
	// That being said, evaluating the display name should still be considered as a "best effort" exercise. (It's not critical or paramount.)
	// For that reason, we call a safe "Try..." wrapper method to ensure that any potential problems we encounter in evaluating the display name
	// don't interfere with our ultimate goal within this code block: evaluation of the condition.
	step.TryUpdateDisplayName(out _);

[ericsciple]

I haven't tested yet 😄

Will look into this during E2E testing (needs server changes to render)